Traffic light signaling sequences or phases are generally controlled by computers or other adjustable or programmable devices that time signaling according to specific schedules. The schedules are designed or selected to accommodate an anticipated traffic flow pattern of vehicles through an associated shared roadway portion, and thereby ensure that vehicles or pedestrians will complete travelling through the shared roadway portion before right of way is granted to another lane or ingress portion, to prevent vehicle collisions, gridlock, etc. Accordingly, transition timing from green through yellow to red light signals within such schedules generally contemplates an anticipated speed of the moving vehicles or pedestrians in order to assure that they will either have time to stop prior to entering, or to clear an affected roadway portion, prior to the signal turning red. For example, the total time to transition from green to red is generally longer on major roads with higher speed limits. Faster moving vehicles need longer stopping distance and lead times, and often may not have enough time or available stopping distance to be able to stop in time to prevent entering an intersection, but must instead proceed through an intersection upon recognizing a yellow signal. Providing for a longer yellow light time period, or otherwise a delayed transition time to red, relative to the same periods given to low-traffic, slower speed limit roadways, thereby allows such vehicles to clear the intersection before another lane is given a right-of-way through a new green signal.
Such timing patterns may be fixed and based on speed limits and anticipated traffic patterns. Different fixed timings may be scheduled, for example selecting one from a plurality of pre-determined timings for low traffic periods, and another different one during rush hour or other time periods with known heavier traffic patterns that provide different signaling for slower vehicle movements due to heavier roadway loading. Timing patterns may also be dynamically controlled, altering fixed traffic signal timing patterns in response to inputs from automobile and traffic flow sensors, such as via real-time inputs from roadway detectors or automated camera system apparatus that enable real-time observations and inferences of overall roadway or intersection loading via vehicle presence detection. For example, observing an extraordinarily large number of automobiles waiting at an intersection in front of a red light, or observing that vehicles are not moving through an intersection, may result in a signal to a traffic signal controller to effect a change in the fixed traffic signal timing pattern to help clear the roadway or intersection. However, differentiated signal timing may be ineffective in relieving other traffic flow impacts and problems beyond routine heavy traffic incidents.